Increase in the number of species (especially broad-leaved weeds) was observed during in situ microbial (CDM) decomposition of rice stubble both in winter (sandy clay loam to clay loam) and rainy (sandy loam) seasons was observed at 60 to 90 days after treatment. Reviewing the literature, faster seed germination of Arabidopsis thaliana and Acacia Senegal seeds treated with Bacillus licheniformis was earlier reported. Azospirillum brasiliense Az39 promoted seed germination through phytohormone synthesis had been reported and in case of Euonymus americanus L. seeds, cellulase activity of cellulolytic ruminal bacterium Clostridium cellobioparum was implicated for the degradation of the testa of the seed, allowing imbibition and germination. Is there any relevant reports for effect of crop residue incorporation on germination of weeds?
I'm not an ecologist but what happened in your control that, e.g. had the enzymes and either no stubble or an artifical, non-degradable 'stubble'?
Dear Dr Paul,
Thanks for your comments. Rice stubble after harvest was treated (in situ) with a solution of glyphosate-microbial culture mixture, glyphosate alone and compared with untreated stuff for decomposition over a four months period. The plots receiving glyphosate-microbial culture mixture (cellulose degrading) showed emergence of significantly higher number of broadleaved and grassy weed species compared to the control (untreated). We did not estimate enzymes (last season), but are doing for dehydrogenase and sufatase this time. Should we analyse additional parameters?
Work at the Rodale Institute shows that stubble can suppress weeds significantly when at sufficient quantity persists a critical time length. The mechanism appears to be related to the shading of the soil surface that does not permit the light triggering of the germination of weed seed. When the residue is over 6,000 kg/ha weed suppression is very significant.
When residue is broken up or fragmented the effect last less. In reality the time of critical need for weed control is the first 30 to 40 days and the use of rolled cover crops is sufficient to provide efficacious weed control with a cover crop roller system.
For a crop like rice the use of winter legume like hairy vetch will provide all the nitrogen need for a crop like rice. The hairy vetch can be killed mechanically by a mechanical roller when hairy vetch is at full flower . If a no till drill is available the system can provide organic no till potential for a rice crop without need for supplemental nitrogen and will good organic weed control. One does need to aware of army worms in that system. In a rye cover crop the winter rye can provide excellent weed control using a no till planting of soybean with a rolled planting.
These organic no till systems incorporating winter cover crops are highly effective in improving the Soil Carbon and Nitrogen values with their continued prolonged use.
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